Newly graduated Marines answer their drill instructors as they graduate from boot camp at the Marine Corps Recruit Depot in Parris Island, S.C. in April. Drill instructors from the base are being investigated for hazing after the death of a recruit.

The Marines have launched an internal investigation into staff at a boot camp in Parris Island, S.C., after Muslim recruit Raheel Siddiqui died in an apparent suicide 11 days after arriving. Fifteen drill instructors are now under investigation, as scrutiny increases of military practices that many believe cross the line from teasing, camaraderie, and toughening-up into danger.

The Parris Island drill instructors face allegations of hazing, assault, and physical abuse, the Marines announced Thursday. The probe into Mr. Siddiqui's death has sparked a wider investigation into wrongdoing in his training unit, known as the "Thumping Third Battalion," as The Wall Street Journal reported.

At the center of the investigation is Siddiqui's senior drill instructor, who was already under investigation for allegedly hazing minority recruits, including putting a previous Muslim recruit into a clothes dryer and making racially charged remarks.

Siddiqui fell three stories off of a stairwell in his barracks in an apparent suicide. His family has said he had no history of mental illness, according to the Journal.

After a week at boot camp, Siddiqui approached his senior drill instructor and said, "This recruit wants to quit and this recruit will commit suicide," according to an incident report the Marines gave to Siddiqui's family. (During boot camp, recruits are expected to speak about themselves in the third person.)

Siddiqui soon retracted that statement and said he was committed to training, however. Medical officials at the camp determined that he "did not have a verified suicidal ideation."

Four days later, Siddiqui passed out in his barracks during an exercise. His parents say investigators told them he had been trying to inform his superior of his deteriorating health, but the superior did not give him the opportunity to do so. After being waken by the senior drill instructor, Siddiqui ran out of the barracks fell three stories after jumping off the stairwell, the Journal reported. He was pronounced dead later that day.

About 12 percent of service members believe hazing is occurring in their units, according to a report released in February from the Government Accountability Office, which concluded that there was no consistent way of tracking military hazing and no clear definition of hazing.

"Despite having anti-hazing policies in place, these policies are unevenly implemented and done with little oversight," Rep. Judy Chu (D) of California, a long-time critic of hazing in the military, told The Washington Post. "In addition, the standards among branches can differ radically, with some not even having a system for collecting data on hazing. We cannot claim that any existing prevention and enforcement policies are adequate without understanding the full scope of the problem."

Fourteen out of 39 men in a Marines focus group reported experiencing hazing, as did eight out of 17 women. All of them, however, said they had received hazing prevention training.

In April, House Rep. Judy Chu (D) of Calif. introduced The Harry Lew Military Hazing Accountability and Prevention Act, which would require the Department of Defense to improve anti-hazing training and improve accountability and reporting. The bill is named for Representative Chu's nephew, who committed suicide after being hazed by his platoon in Afghanistan in 2011.

Maj. Gen. James W. Lukeman, commanding general of Marine Corps Training and Education Command, said in a statement that they were taking the matter seriously and investigating thoroughly.

"The safety of the recruits and the integrity of the Marine Corps recruit training program are among our top priorities and, once the investigations are complete, we will take necessary administrative and judicial action as warranted to ensure proper accountability," he said, according to The Chicago Tribune.